The present invention relates to a method of obtaining the temperature of an object being heat treated and, more particularly, to a method of determining the temperature of an object moving along with a hearth through a heat treating furnace.
Industrial heat treating furnaces capable of heat treating large cast metal objects such as railway wheels are themselves fairly large. A preferred design of such heat treating furnaces is of a circular configuration. Such a circular configuration permits the continuous movement within the furnace of a ring shaped insulated hearth. The furnace itself is comprised of a ring shaped insulated heated area having heating means such as gas burners located both on the inner side and outer side of the ring shaped insulated heated area. A charging door and a discharging door are usually located adjacent each other on an outer surface of the ring. The charging door is utilized to insert the objects such as railway wheels into the heating area of the furnace and onto a support on the movable hearth. Typically such furnaces can accommodate about ninety railway wheels, and the hearth rotates within the furnace at such a speed so as to expose each wheel to about a two-hour heat treating operation. Although it is a fairly straight forward matter to monitor the temperature of particular zones within the heat treating furnace insulated area, it has been a problem to provide a continuous temperature determination of each object being heat treated as it moves throughout the furnace. Depending on the desired properties to be obtained during the heat treating process, it is desirable to have such an accurate temperature determination available at all times during the objects travel through the heat treating furnace. A prior method was to attach a thermocouple wire to the object being heat treated and to allow the object to travel throughout the furnace feeding additional thermocouple wire through the charging door into the furnace as the hearth rotated. This method was undesirable due to the use of extremely long runs of costly thermocouple wire which had to run the entire circumference of the heat treating furnace. As a typical diameter for such furnaces is about 70 feet (21 meters), making a total circumference of about 220 feet (67 meters), the length of thermocouple wire is rather long. Such wire can be used only once and accordingly, presents a rather high expense. In addition, due to the long run of thermocouple wire through the furnace, there is a great possibility of errors in the temperature readings.